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/*-------------------------------------------------------------------------
*
* tuptoaster.h
* POSTGRES definitions for external and compressed storage
* of variable size attributes.
*
* Copyright (c) 2000, PostgreSQL Development Team
*
* $Id: tuptoaster.h,v 1.11 2001/05/07 00:43:24 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef TUPTOASTER_H
#define TUPTOASTER_H
#include "access/heapam.h"
#include "access/htup.h"
#include "access/tupmacs.h"
#include "utils/rel.h"
/*
* This enables de-toasting of index entries. Needed until VACUUM is
* smart enough to rebuild indexes from scratch.
*/
#define TOAST_INDEX_HACK
/*
* These symbols control toaster activation. If a tuple is larger than
* TOAST_TUPLE_THRESHOLD, we will try to toast it down to no more than
* TOAST_TUPLE_TARGET bytes. Both numbers include all tuple header and
* alignment-padding overhead.
*
* The numbers need not be the same, though they currently are.
*/
#define TOAST_TUPLE_THRESHOLD (MaxTupleSize / 4)
#define TOAST_TUPLE_TARGET (MaxTupleSize / 4)
/*
* If an index value is larger than TOAST_INDEX_TARGET, we will try to
* compress it (we can't move it out-of-line, however). Note that this
* number is per-datum, not per-tuple, for simplicity in index_formtuple().
*/
#define TOAST_INDEX_TARGET (MaxTupleSize / 16)
/*
* When we store an oversize datum externally, we divide it into chunks
* containing at most TOAST_MAX_CHUNK_SIZE data bytes. This number *must*
* be small enough that the completed toast-table tuple (including the
* ID and sequence fields and all overhead) is no more than MaxTupleSize
* bytes. It *should* be small enough to make toast-table tuples no more
* than TOAST_TUPLE_THRESHOLD bytes, else heapam.c will uselessly invoke
* the toaster on toast-table tuples.
*
* NB: you cannot change this value without forcing initdb, at least not
* if your DB contains any multi-chunk toasted values.
*/
#define TOAST_MAX_CHUNK_SIZE (TOAST_TUPLE_THRESHOLD - \
MAXALIGN( \
MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) + \
sizeof(Oid) + \
sizeof(int32) + \
VARHDRSZ))
/* ----------
* heap_tuple_toast_attrs() -
*
* Called by heap_insert(), heap_update() and heap_delete().
* Outdates any no-longer-needed toast entries referenced
* by oldtup and creates new ones until newtup is no more than
* TOAST_TUPLE_TARGET (or we run out of toastable values).
* Possibly modifies newtup by replacing the t_data part!
*
* oldtup is NULL if insert, newtup is NULL if delete.
* ----------
*/
extern void heap_tuple_toast_attrs(Relation rel,
HeapTuple newtup, HeapTuple oldtup);
/* ----------
* heap_tuple_fetch_attr() -
*
* Fetches an external stored attribute from the toast
* relation. Does NOT decompress it, if stored external
* in compressed format.
* ----------
*/
extern varattrib *heap_tuple_fetch_attr(varattrib *attr);
/* ----------
* heap_tuple_untoast_attr() -
*
* Fully detoasts one attribute, fetching and/or decompressing
* it as needed.
* ----------
*/
extern varattrib *heap_tuple_untoast_attr(varattrib *attr);
/* ----------
* toast_compress_datum -
*
* Create a compressed version of a varlena datum, if possible
* ----------
*/
extern Datum toast_compress_datum(Datum value);
/* ----------
* toast_raw_datum_size -
*
* Return the raw (detoasted) size of a varlena datum
* ----------
*/
extern Size toast_raw_datum_size(Datum value);
#endif /* TUPTOASTER_H */
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